Graffiti on windows in public areas has been a longstanding problem, particularly for windows on public transportation systems, such as subways and buses. One solution to the problem of graffiti on windows has been the mounting of transparent shields or guard panels on the windows. When such a device is installed, graffiti collects on the shield rather than the window. These graffiti shields are typically plastic and disposable. The windows themselves are often much more expensive to replace than a disposable plastic graffiti shield. When an undesirable amount of graffiti is present on the shield, the shield can be removed, disposed of and replaced without replacing the window.
There have been various approaches to mounting the graffiti shields over the windows. One solution has been to use retaining strips which hold the graffiti shield over the window by clamping the edge of the shield between the strips and the window or the frame. The retaining strips are generally held to the frame with fasteners such as screws. By tightening the screws, the strips hold the graffiti shield in place. Another solution has been to use double-sided tape. The tape is applied directly to the face of the graffiti shield and then the shield is attached to the window or to the frame. Still another approach has been to install a new window frame that will hold both the graffiti shield and the window in place.
Each of these solutions to the problem of mounting the graffiti shield over the window have significant disadvantages. Using retaining strips held in place by screws is inefficient because the initial installation of the strips is difficult and expensive. In addition, replacing the graffiti shield is time consuming, as at least one of the strips must be completely removed by unscrewing the screws one by one. Moreover, after the graffiti shields have been replaced a number of times, the threads on the retaining strips or the mounting for the retaining strips can become worn and eventually stripped. This can require the frequent replacement of the strips and eventually the mounting for the strips as well.
The use of double-sided tape has some advantages in that the installation replacement and maintenance can be simplified. However, the graffiti shield panel itself or such a system is generally more expensive than the simple panel which can be used with the retaining strips. Another drawback to the use of double-sided tape is that the removal of such tapes often leaves a residue behind which can be difficult and time consuming to remove.
The use of a window frame that holds both the window and the graffiti shield permits the rapid replacement of a graffiti shield, but initial installation is costly and time consuming.
Also, there are installation difficulties inherent in a dual glaze bus window system. The largest single problem is moisture intrusion between the two glazing plies. If there is an insufficient gap between the two plies, the water and/or moisture that may get in between the plies due to washing or normal condensation processes, may not drain properly. If this should occur and the trapped water cannot drain out properly, visibility through the window can be impaired. Furthermore, water buildup can lead to the formation of salt or calcium deposits between the window and the window shield which can further impair the clarity of both the window and the window shield.
Another problem typical in a dual glaze bus window system is that the graffiti shield is generally made of a relatively soft material, such as acrylic. If that material comes into contact with the structural glazing, such contact can create clouding or scratching due to the abrading of the window guard by the glass.
A solution that would allow the easy installation and replacement of inexpensive window shields, that would provide either a better seal between the existing window frame and the window shield or permit proper drainage of any trapped moisture that accumulates between the window shield and the window, and that would keep the window protector and window sufficiently apart to prevent a damaging interaction between the two, would be an improvement in the art and of great public value.
While quick change windows and window frames including window protectors are becoming available, the cost of retrofitting an entire vehicle with such devices is often very high. Therefore, a solution which would provide a less expensive method of retrofitting existing window frames to permit the use of quick change window shields would be an improvement in the art and of great public value.